The Anthropocene: a futurist perspective
Valentí Rull
Post-print revisado y aceptado por Sage Journals el 12 de febrero de 2013.
Palynology and Paleoecology Lab
Botanic Institute of Barcelona (IBB-CSIC-ICUB)
Pg. del Migdia s/n, 08038 Bacelona, Spain
Phone +34 2890611, fax +34 2890614
E-mail: [email protected]
Abstract
The ongoing debate about the acceptance of the Anthropocene as a formal
chronostratigraphic unit with the same rank as the Holocene (epoch) has centered on
either the existence or the lack of a Global Stratotype Section and Point (GSSP). In this
paper, it is proposed that this may not be a major problem, as their discovery and
definition could only be a matter of time. However, the term Anthropocene itself,
defined on the basis of the stratigraphic expression of human activities (e.g., large-scale
agriculture and land clearance, accelerated release of greenhouse gases to the
atmosphere) may significantly impact the current stratigraphic framework guided by the
International Commission on Stratigraphy (ICS). Indeed, the formal usage of this term
not only can lead to stratigraphic and terminological inconsistencies but also can
influence the future development of the established chronostratigraphic scheme as well.
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These points should be considered by the ICS Anthropocene Working Group before
making a final decision. The stratigraphic status of the Anthropocene, however, is a
formal issue that should not affect current and future research on human-induced
environmental and sedimentary changes, including their stratigraphic imprint. The
message is twofold: leave the formal chronostratigraphic aspects to the ICS, and keep
producing and organizing knowledge independently of the formal debate. Doing so
would require the development of a parallel and likely transitory chronological system
without formal stratigraphic value, from which the term Anthropocene should be, at
least temporarily, excluded.
Keywords Anthropocene, Holocene, chronostratigraphy, chronology, human impact,
industrialization
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Introduction
In a recent Holocene paper entitled “The stratigraphic status of the Anthropocene”, Gale
and Hoare (2012) discuss the validity of the term Anthropocene as a formal
stratigraphic unit and conclude that the definition of this epoch is unnecessary and
arbitrary. They base this conclusion on the fact that the Anthropocene does not fulfill
certain keystone conditions to qualify as a formal unit, namely the existence of a Global
Stratotype Section and Point (GSSP) through the precise definition of an isochronous
datum that marks a critical change in the sedimentary sequence (golden spike) that can
be considered the boundary between two epochs (i.e., the Holocene and the
Anthropocene) and identifiable elsewhere. In particular, Gale and Hoare (2012) criticize
the proposal of Certini and Scalenge (2011), stating that soils affected by human
activities (anthrosoils or anthroposoils) would be the best markers for the beginning of
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the Anthropocene. According to Gale and Hoare (2012), soils fail to meet at least nine
criteria for the establishment of stratigraphic datums, notably their poor preservation
potential, and many environments do not experience pedogenesis, thus making global
correlations impossible. In addition, the basal date of anthropogenic soils is often
difficult to define and is markedly diachronous at a global level. Therefore, the main
handicaps to accepting the Anthropocene as a formal unit remain, namely, the lack of a
global stratotype and the difficulties in locating a global isochronous datum that could
be considered the golden spike to define the Holocene/Anthropocene boundary (Gale
and Hoare, 2012). At present, the convenience or inconvenience of including the
Anthropocene in the current chronostratigraphic framework is under debate by the
organizations in charge of validating stratigraphic units (Zalasiewicz et al. 2011a).
Indeed, the International Commission of Stratigraphy (ICS), through the
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Subcommission on Quaternary Stratigraphy, has created the Anthropocene Working
Group (AWG, 2012) to address this issue.
This paper analyses the main points raised by Gale and Hoare (2012), namely,
the issue of the golden spike and the global stratotype, from a general conceptual and
theoretical perspective. Emphasis is placed on the concept of diachronism and its
relationship with dating precision. The convenience or inconvenience of the definition
of the Anthropocene as a formal chronostratigraphic unit is also discussed, not only in
terms of past and present evidence but also in terms of future prospects for human
existence on Earth and the potential stratigraphic consequences. Terminological issues
are also considered under the same perspective.
The onset of the Anthropocene
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Before analyzing the topic from a theoretical point of view, it would be useful to briefly
introduce the existing proposals for the onset of the Anthropocene. The Anthropocene
was originally defined as the geological epoch characterized by the conspicuous imprint
of human activities on the Earth’s surface and on atmospheric processes (Crutzen,
2002). Therefore, the key point in defining the beginning of the Anthropocene is
determining when the consequences of human activities started to be evident on the
planet.
The first markers were considered to be the increase in carbon dioxide and
methane in ice cores, significant changes in biological assemblages in lake sediments,
or the deposition of artificial isotopes produced by nuclear weapons, all of them having
occurred during the last two centuries and being related to industrialization (Crutzen,
2002; Zalasiewicz et al., 2008; Steffen et al., 2011; Wolfe et al., 2013). Steffen et al.
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(2007) subdivided the Anthropocene into two stages: Stage I (AD 1800-1945), or the
Industrial Era, and Stage II (AD 1945-2015), or the Great Acceleration, characterized
by a sudden increase in human population after the Second World War and a growth in
petroleum consumption by a factor of 3.5. According to Gale and Hoare (2012),
however, such a definition of the Anthropocene and its stages is based on chronometric
rather than chronostratigraphic indicators and, as such, it cannot be used to formally
define an epoch. A very recent review of the evidence from arctic and alpine lake
sediments proposes that the Holocene-Anthropocene transition should be placed around
AD 1950, almost coinciding with the onset of the Great Acceleration (Wolfe et al,
2013). The authors favor this date, which is approximately one century older that the
onset of the atmospheric CO2 increase due to fossil fuel combustion because
sedimentary changes in the lakes studied show a clear stratigraphic marker that would
serve as a global datum (the golden spike), as required for the ICS to accept the
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Anthropocene as a formal unit.
A contrasting view has been provided by those who locate the beginning of the
Anthropocene at the early (ca. 8000 y BP) or the middle (ca. 5000 y BP) Holocene,
respectively based on increases in carbon dioxide or methane as a by-product of human
activities, such as widespread rice cultivation or pre-industrial land clearance
(Ruddiman, 2003). However, the possibility of these changes being a consequence of
natural forcings has also been suggested in a recent Holocene special issue dedicated to
“The Early-Anthropocene Hypothesis” (Ruddiman et al., 2011).
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Diachronism and dating precision
Synchronism and diachronism may be a matter of scale. Geological ages ultimately rely
on radiometric methods, although geochronological correlations use a variety of
intermediate well-dated markers. Biostratigraphy, based on the first and last
evolutionary appearances (FAD and LAD, respectively) of index taxa, is the more
widely used tool to chronologically correlate stratigraphic units (Gradstein et al., 2004).
Both radiometric and biostratigraphic dating, however, are subject to inherent errors.
Radiometric errors are linked to methodological constraints and are expressed
statistically as confidence intervals. Biostratigraphic errors are due to the intrinsic
diachronic nature of FADs and LADs, due to lags in biological processes and
phenomena, such as differential dispersal ability, which influences FADs, or
environmental tolerance leading to local extinction, which affects LADs. These
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biological errors are rarely mentioned in correlation studies and occur at similar time
scales (typically centennial to millennial), no matter the boundary under study. The
magnitude of methodological and biostratigraphic errors, in relation to the absolute
dates measured, is critical for these dates to be accepted. For example, errors that are
millennial magnitude are very welcome when dating the Cretaceous/Paleocene
boundary (e.g., Batenburg et al., 2012) at ~65 Ma, but they are unacceptable if the
dating target is the Pleistocene/Holocene boundary, approximately 11,700 y BP (Walker
et al., 2009). Large-scale correlations based on such errors follow the same rules.
In the case of the Anthropocene onset, as currently defined, the dating precision
should be remarkably lower than a century (ideally, less than a decade), which is
difficult to achieve. In addition, most recent sediments are still unconsolidated and are
poorly packed, which hampers the discovery of well-defined lithostratigraphic
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correlation boundaries (Zalasiewicz et al., 2011b). Exceptions to these rules are the
special cases of laminated sediments and ice cores, whose precision might attain the
seasonal scale. However, this situation could be generalized to any boundary of the
chronostratigraphic framework. In other words, the same problems may be encountered
when trying to date, for example, the Miocene/Pliocene boundary (~5.3 Ma) just a
couple of centuries after its occurrence (if this were possible). With time, the sediments
are progressively accumulated and consolidated, the boundaries better defined and, what
is more important, the errors required for sound dating and correlation greater. It
follows that, with time, the eventual Holocene/Anthropocene boundary will be better
dated—and the corresponding stratigraphic markers correlated—than they are today
(Zalasiewicz et al., 2011b). This does not mean that the respective boundaries will be
less diachronic, just that this diachronism will be less significant with respect to the
dating errors. Therefore, satisfactorily dating the onset of the Anthropocene may be only
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a matter of time. Meanwhile, efforts such as those of Wolfe et al. (2013), who attempted
to identify this boundary over vast regions and to propose better potential markers, are
worth making. Laminated sediments are especially well suited for this purpose because,
despite their scarcity, they are relatively well distributed for attempting global
correlations (Ojala et al., 2012). Thus far, the thin sedimentary layer reflecting human
impact does not appear to be easily discernible from an anomaly (Zalasiewicz et al.,
2011b), especially if the Holocene/Anthropocene boundary is located around AD 1950
(Wofe et al., 2013), but time will confirm whether it attains the rank of a distinct,
widespread and chronologically consistent sedimentary unit.
Therefore, under a futurist perspective, the Anthropocene seems to resist the
argument of the lack of a golden spike to be properly defined.
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The Anthropocene and the future
Contrary to other chronostratigraphic units of the same hierarchy—as, for example, the
Paleocene and Miocene, for which the onset and the end are reasonably well known and
dated—the Anthropocene, as currently defined, is still in the making. This adds
difficulties to its definition as a chronostratigraphic unit until the next one begins. By
definition, the Anthropocene is based on the recognizable impact of human activities in
the stratigraphic record; therefore, its end is implicitly defined by the end of such a
scenario. As the end of a chronostratigraphic unit is defined by the beginning of the next
one (Murphy and Salvador, 1999), a precise definition, age and duration of the
Anthropocene will require the replacement of visible human impact by another
dominant force that can be embodied in the fossil record, which could happen with or
without humans inhabiting the Earth. In the first case, one possibility is the coming of
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the next glaciation, which, according to recent estimations, would occur naturally within
approximately 1500 years (Tzedakis et al., 2012). In general, any environmental or
internal (auto-induced by humans) event leading to a significant reduction of human
influence on global surface processes has the potential to be a candidate. In the second
case, such an event should be catastrophic and would eradicate humanity from Earth. A
third possibility is that human influence dominates until our evolutionary disappearance,
likely a matter of millions of years (Rull, 2009). Of all these possibilities, the
Anthropocene, and the rest of the chronostratigraphic units, will only make sense if
humans remain on Earth and use the same geological framework as today.
The Holocene poses (or posed, for those who favor the Anthropocene as an
epoch) a similar situation, but its identity is not as strongly influenced by its name.
Indeed, the meaning of the Holocene is “entirely recent” or “recent whole”, a name that
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does not implicitly involve any driving force or causal context. The Holocene has been
defined in climatic terms as the current warm period and, based on past records, is
considered the interglacial following the last glaciation (Walker et al., 2009). This
definition is more constraining and implicitly places the end of the Holocene at the start
of the next glaciation. This view is not shared by those who propose that the impact of
humanity on the Earth’s climate is capable of indefinitely postponing the onset of the
next glaciation (Ruddiman et al., 2005; Steffen et al., 2007). If humans were capable of
modifying the glacial-interglacial alternation in such a way, the Anthropocene would be
the last epoch of the current stratigraphic framework, unless other environmental forces,
as for example major tectonic and volcanic events, would overcome the stratigraphic
signature of human disturbance. In this case, the Anthropocene would likely last
millions of years, and its subdivision should follow the different types of human forcing
with a recognizable stratigraphic imprint.
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In light of this discussion, perhaps it is still too soon to decide about the
acceptability of the Anthropocene as a formal epoch; further evidence is needed to
validate this proposal. The time needed to do so seems to be very long in relation to the
human life cycle; hence, the issue should be postponed and left to future generations. A
premature acceptance would close down the current stratigraphic scheme, with
uncertainty over whether it should be opened again in the future.
Terminological notes
There is a general consensus that the world has changed recently due to human activities
and that this is reflected not only in the climate and other atmospheric and surface
processes but also in a variety of sedimentary markers. The real problem seems to be
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terminological, i.e., the use of the suffix –cene, which implicitly places the
Anthropocene within the current chronostratigraphic framework as an epoch, before an
ICS pronouncement. Using quotation marks or recurrently insisting on the informal
nature of the term has not helped settle the issue, and the debate continues. One
potential solution is to use a term of a clearly informal nature and to change it to
Anthropocene, provided the new term is formally accepted in the future. Unfortunately,
the solution is not so simple. Using either term may have important conceptual
implications. One is that the use of Anthropocene, as an epoch, implies that the
Holocene has ended, which is incompatible with the definition of the Holocene as the
present interglacial. The question here is whether both the present interglacial and the
Holocene should be redefined. Alternatively, if the Holocene maintains its rank as the
present interglacial, then the Anthropocene would be part of the Holocene, as an age,
and their names would be changed by replacing the suffix –cene by –ian to read
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“Anthropocenian” or something similar. This option implies that the next glaciation will
be able to impose its stratigraphic signal over the human one, whatever the reason. In
this case, the question is whether Anthropocenian-like stages would be recurrent in each
interglacial and, if so, what the correct term would be to refer to them (Anthropocenian1, -2, -3?). The same would be true for the Anthropocene if the stratigraphic
consequences of further glaciations prevail over the human signal.
Choosing alternative informal names is also problematic. When using an
informal term, any suffix with accepted meaning within the official chronostratigraphic
framework should be avoided. For example, the term “Anthropogene” was created as a
synonym of Quaternary, considered as a period, with the same rank as Paleogene or
Neogene (Gerasimov, 1979). This option has not been validated by the ICS, but the
term should be excluded from the potential options to avoid confusion. Another
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possibility would be the use of Great Acceleration, but this was originally defined as a
stage of the Anthropocene (Steffen et al., 2007) and would also be misleading. Rather
than clarifying the issue, creating new informal names would further complicate the
picture. An alternative would be to employ the well-known and frequently used term
“industrialization”, borrowed from the history of economy, including both the Industrial
Era and the Great Acceleration of Steffen et al. (2007). An advantage of this term is that
it opens the possibility of differentiating among industrial and other types of human
impact on the stratigraphic record, thus bypassing the problem mentioned above on the
need for human demise to properly define the corresponding GSSP. In addition, this
terminological framework would reconcile the current definition of the Anthropocene as
restricted to the last two centuries (Crutzen, 2002), with the hypothesis of the early to
mid-Holocene onset (Ruddiman, 2003), which could be referred to using common
historical and anthropological terms such as “agriculture expansion” or “pre-industrial
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clearance”, provided there are clear and synchronic stratigraphic markers defining
distinct sedimentary bodies. Otherwise, these terms would constitute a parallel
chronologic system without any formal stratigraphic value (Gale and Hoare, 2012), but
would be equally useful.
In summary, terminology is not only a matter of words but also of what the
words imply in terms of present and future stratigraphic developments. The compulsive
idea of attachment to the official stratigraphic scheme would create more problems than
solutions, and some alternatives exist to ease this tension.
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Escaping the stratigraphic rules?
Gale and Hoare (2012), among others, question the need for a definition of the
Anthropocene as a new epoch, arguing that its usefulness is doubtful and that “the
global stratigraphic approach as a whole may eventually prove of limited practical use
in studies of human environmental impact” (p. 1494). As in other case studies, such as
the recently debated Quaternary (Aubry et al., 2009; Gibbard et al., 2009), the resistance
of some geological sectors to include modifications in the chronostratigraphic
framework have been interpreted as a negative attitude. This is not the case. For new
stratigraphic units to be included in the current ICS framework, the ICS rules should be
fulfilled, as occurs in any other normative organization or activity. If, finally, the AWG
decides that the Anthropocene should not be considered an epoch following the
Holocene, this does not mean that they are denying the influence of human activities on
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the Earth system; it only means that the available chronostratigraphic evidence is not
enough to declare the Holocene officially dead and to define a new epoch after it. If
further research eventually provides more conclusive evidence, then the decision could
be reconsidered.
The above-quoted sentence of Gale and Hoare (2012) should not be taken as a
rejection but as an opportunity to bypass the ICS stratigraphic rules while the ICS
discusses the final decision. Indeed, the message is that it is not necessary to formally
define the Anthropocene as an epoch to accept that human activities have significantly
changed the earth system processes during the last two centuries. In other words, studies
on the changes due to human impact, including stratigraphic changes, are independent
of whether the Anthropocene is recognized as a formal epoch within the ICS
framework. Therefore, the battle for such recognition does not seem to be very
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productive at present. As discussed above, the resolution of this issue may only be a
matter of time. Perhaps it would be better to conserve efforts and concentrate on the
study of the involved processes, the potential consequences and their sedimentary
imprint, whatever the current stratigraphic status of the Anthropocene. In the end, all the
information gathered in this way will help the ICS make a better decision.
If necessary, the development of a parallel chronological framework without
formal stratigraphic value, as suggested above, will suffice. Knowledge advancement
should not be constrained by the existence (or not) of formal chronostratigraphic terms
to account for it. Such a chronological system, however, should avoid the term
Anthropocene because of its implicit formal chronostratigraphic meaning.
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